This invention relates generally to propulsion systems and, more particularly, to a gear shift mechanism for a marine propulsion system.
Mechanical propulsion systems for propelling watercraft generally are classified as either outboard systems or inboard systems. Outboard systems typically are characterized by an outboard motor mounted to a vertical transom plate located on an outside stem of a boat hull. A propeller drive unit is attached to the motor, or powerhead, and extends from the powerhead into the water to generate thrust and propel the watercraft. Outboard motor systems are versatile, compact, and cost-effective units that are relatively easy to install on the boat hull. Also, because the outboard system is attached to the outside of the hull, the outboard motor system generally does not occupy interior space of the boat hull. However, due to structural constraints of the vertical transom plate mounts of outboard systems, watercraft with outboard systems are typically limited to certain motor capacities within size and weight constraints.
Inboard systems are typically characterized by larger, complicated, and relatively expensive engines in comparison to outboard systems. Inboard system engines are mounted in an engine compartment in a boat hull interior, and a drive unit, or stem drive, extends through a vertical wall of the boat hull into the water to generate thrust and propel the watercraft. Inboard systems, however, are much more complicated to install in a boat hull, which further increases the cost of a watercraft. Furthermore, bulky inboard engines and engine compartments often occupy a substantial amount of interior hull space due to the proximity of the engine compartment to a running surface of the hull.
Moreover, known gear shift mechanisms for marine propulsion systems, such as shift lever, cable and hydraulic systems are relatively intricate and difficult to water seal.
In an exemplary embodiment of the invention, a gear shift mechanism for a marine propulsion system includes a reversible DC electric motor, a sliding clevis, and a shift rod for actuating a gearset within a gearcase between forward, reverse, and neutral positions. The mechanism is housed in a watertight gear shift cover that is attached to a top surface of the gearcase. Electronic, logic driven controls reverse the polarity of the motor to manipulate the shift rod via the sliding clevis to shift the gearcase into a selected operating position. In one embodiment, the gearset includes gear reduction that allows a fractional horsepower motor to be used to actuate the clevis and shift rod.
In an exemplary embodiment, the gear shift mechanism is part of a marine propulsion system including an outboard propulsion system powerhead mounted to a horizontal mounting plate in an outside engine compartment formed into a platform extending from a boat hull. The engine compartment is enclosed by an engine cover at a stern of a watercraft. The marine propulsion system includes an upper unit that includes the powerhead and a lower unit that includes a propeller drive unit. A four point mounting assembly eases installation of the upper and lower units and absorbs vibration of the upper and lower units to produce smooth, quiet propulsion of a watercraft. The outboard powerhead is mounted stationary to the horizontal mounting plate, and a steering arm yoke and trunnion assembly is attached to the horizontal mounting plate and extends outside of the boat platform to maneuver the watercraft.
The gear shift mechanism is attached to the lower drive unit below the horizontal mounting plate and rotates, trims, and tilts with the propeller drive unit, at or below the waterline when the boat is in the water. Electronic, logic driven controls reverse the polarity of the motor in the watertight housing and rotate a motor shaft to manipulate the sliding clevis and shift rod to actuate the gearset between forward, reverse, and neutral positions. Thus, a compact, watertight and relatively simple gear shift mechanism is provided in lieu of known shift lever, hydraulic, and cable systems that are relatively complicated and difficult to water seal.
Thus, the gear shift mechanism and the marine propulsion system provide the versatility, compactness and cost savings of an outboard powerhead with the stability and performance advantages of an inboard system. Structural limitations and instability of vertical transom plate mounts are avoided by mounting the outboard powerhead to the horizontal mounting plate in the boat platform.